This section provides background information related to the present disclosure which is not necessarily prior art.
Sway bars or anti-roll bars are used in vehicles to adjust the torque of the suspension system which then influences the roll rate. Sway bars are typically torsional springs which act across an axle to introduce resistance to relative changes in the displacement of one wheel on the axle compared to the displacement of the other wheel on the same axle. The sway bar or torsion spring is constrained both radially and axially and it is connected to the suspension member by a lever arm or by a linkage. The torsional spring rate of the sway bar contributes to the roll stiffness for the vehicle. The lever arm or the linkage acts as a spring element which is designed to allow for compliance of the axle to the frame in the lateral direction.
Roll stiffness is important to both the ride comfort and the cornering ability of the vehicle. Too little roll stiffness results in excess body roll or lean and slow response to the rotation of the steering wheel by the driver. On the other hand, too much roll stiffness creates an uncomfortable ride and can cause a sudden loss of traction and the ability of the tires to stick to the road during cornering maneuvers.
FIG. 5 illustrates a typical prior art sway bar assembly 100. Sway bar assembly 100 includes a center spacer bar or torsional spring 102 and a pair of lever arms 104 attached to the opposite ends of center spacer bar 102. Center spacer bar 102 is attached to the frame using a pair of elastomeric bushings 106. The ends of center spacer bar 102 include an enlarged portion 108 which facilitates the connection of lever arms 104. Lever arms 104 are welded to enlarged portions 108 and enlarged portions 108 provide for an increase in the length of weld between lever arms 104 and center spacer bar 102. The ends of lever arms 104 opposite to center spacer bar 102 are attached to an elastomeric bushing assembly 110 which is utilized to connect lever arms 104 to the axle of the vehicle. Each elastomeric bushing assembly 110 includes an outer housing 112, a center pin 114 and an elastomeric bushing 116 disposed between outer housing 112 and center pin 114.
There are several critical issues for the design of sway bar assembly 100. The welding between lever arms 104 and center spacer bar 102 are critical. Should this weld fail, the system fails and the control and handling of the vehicle would be compromised. Lever arms 104 act as spring elements which are designed to allow for compliance of the axle to the frame in the lateral direction. Lever arms 104 are typically manufactured from complex alloy steels which are developed to withstand the frequent cycle loading which occurs during normal operation. Lever arms 104 are relatively thin in the vertical direction to allow for flexing of lever arms 104 to provide the necessary lateral compliance. Typically, to increase the fatigue strength of lever arms 104, a shot peening process is performed to introduce compressive stresses in the surface of lever arms 104. Any failure of lever arms 104 will cause the loss of the complete function of sway bar assembly 100. Should there be a failure of one of lever arms 104, the individual lever arm 104 cannot be replaced, the entire sway bar assembly 100 must be replaced. Also, to provide adequate strength for sway bar assembly 100, complex heat treatment of lever arms 104 and center spacer bar 102 is required. Typically, this heat treatment is performed after the welding of lever arms 104 to center spacer bar 102 making it bulky and difficult to handle through the heat treatment process. This makes it susceptible to warpage which requires a complex fixture during the heat treatment process and the possibility that a post heat treatment straightening operation is required at added expense.